For cargo transport, the Byzantines usually commandeered ordinary merchantmen as transport ships (phortēgoi) or supply ships (skeuophora). These appear to have been mostly sailing vessels, rather than oared.

A big thank you to the crew for allowing me to take a picture prior departure! The "bobby" cockpit is always a treat to look at. - Photo taken at Frankfurt am Main (Rhein-Main AB) (FRA / EDDF / FRF) in Germany in May,